I understand that this is for user safety and easier development, but please include an "I am ready for any risks and aware of my actions" mode in the stable version.
If you visit https://addons.mozilla.org/en-US/firefox/ on your phone (instead of https://addons.mozilla.org/en-US/android/), I don't think there is anything that would prevent you from installing a desktop version of an extension on your phone. Desktop versions may not work or may have some UI issues on mobile, but you should still be able to install them. Are you not able to do this?
Sorry I left out an important detail, you have to toggle on "Desktop site" to do this.
Regarding the idea you linked to, I am primarily focused on our adds-on space rather than the browser itself. I will make sure to surface this idea with the appropriate team.